mod-circulation v19.2.0 memory leaks

Overview:
mod-circulation v19.2.0 seems to have an easily reproducible memory leaks issue. When starting up the module without sending any requests to it, mod-circulation gobbles up memory, from 60% to 100%. When put it under a 8-users check-in-check-out test, mod-circulation continually taking memory without putting it back, resulting in the Docker containers crashing after 30 minutes of running the test. Longevity test of v19.1.0-SNAPSHOT also showed leaks, but slower than 19.2.0. Heap dump of memory leaks showing HTTPClientImpl objects being the main culprit.

Steps to Reproduce:

1. Run any repetitive workflow tests, get RTAC or check in/out with 1-8 users for half an hour and mod-circulation's memory utilization will increase easily.

Expected Results:
No memory leaks observed
Actual Results:
Memory leaks observed, docker containers crashed in a 30 minutes test.

Additional Information:
URL: Please see the last comment by Roman Fedynyshyn on PERF-123 detailing the findings of mod-circulation v19.2.0 memory leaks.
Interested parties: marcjohnson cboerema